This invention relates to a fault sensing control circuit for power systems and the like and more particularly to such a control circuit having current sensing means for controlling power line switchgear.
Power distribution systems normally include automatic circuit breakers which respond to various overcurrent conditions. For example, U.S. Pat. No. 3,739,229 to Richard J. Moran discloses a distribution system employing an improved repeating circuit interrupter. As more fully disclosed therein, the interrupting circuit is constructed to respond to overcurrent line conditions and/or a ground fault condition in the electrical distribution system. In distribution systems, the faults may be of a temporary nature which will automatically clear, in which case a mere momentary opening of the circuit system is all that is necessary, after which the circuit can be reestablished. Certain abnormal conditions may be so severe that practically instantaneous response is required. In other instances, the faults are of a temporary characteristic or nature and will automatically clear. They may be of a transient characteristic and of such short duration that they will not adversely affect the equipment tied to the line or the like. The control circuit should, therefore include a minimum response control to permit such faults without actuating of the control. The various restrictions and conditions encountered have required development of relatively sophisticated control circuitry for operating of various interrupters in circuit breakers. Further, the switchgear should be flexible to permit application to various facets of the protection system required. Thus, certain installation may require a control circuit which responds to only ground faults while another only to line current faults and still another to both. Although such systems are clearly justified by the damaging results which follow without adequate line protection, such sophistication does generally result in substantial increased cost. There is, however, a continuing need for improved reliability and decreased costs in the control circuitry for line distribution switchgear.